1. Field of the Invention
The present invention relates generally to a linear motion guide unit adapted for use in various types of machinery such as semiconductor manufacturing machines, precision measuring instruments, precision assembly machines and, more particularly, to a linear motion guide unit in which a slider is movable on an elongated track rail by virtue of rolling elements that are allowed to run through recirculating passages, together with separating elements each arranged between any adjacent rolling elements.
2. Description of the Prior Art
Although current linear motion guide units have been used extensively in diverse fields of machinery such as machine tools, semiconductor manufacturing equipment, conveying systems, inspection instruments, measuring means, processing systems, assembly machines, various industrial robots, and so on, the scope of their useful applications is still expanding with the development of technology. To this end, the linear motion guide units are seeing growing demands for less noise or vibration, reduction of wear, long-lasting service life, high precision, high-speed sliding motion, easy assembly, generally accepted usage, and so on. In recent years, especially, the linear motion guide unit is much expected in which separators are each interposed between any two adjoining rolling elements to lower noise, reducing wear thereby realizing long-lasting service life.
A linear motion guide unit as shown in FIG. 16 is disclosed in, for example Japanese Patent Laid-Open No. 12465/2001. The prior linear motion guide unit is generally composed of an elongated track rail 41 and a slider 42 that fits over the track rail 41 for linear movement along the track rail 41. Raceway grooves 47 are made on lengthwise sides 43 of the track rail 41, one to each side. Moreover, the track rail 41 is made on a top surface 45 thereof with openings 46 in which bolts fit to fasten the track rail 41 on any of a bed, machine base, and so on. The slider 42 is comprised of a carriage 44 fitting over and conforming to the track rail 41, end caps 48 secured on forward and aft ends of the carriage 44, one to each end, and end seals 49 arranged on lengthwise outermost faces of the end caps 48 to close clearances between the track rail 41 and the end caps 48. Fastening screws 51 are to join together both the end caps 48 and the end seals 49 to the carriage 44, while sidewise opposing bottom seals 52 are arranged underneath both the carriage 44 and the end caps 48. The carriage 44 is made therein with raceway grooves 53 confronting the raceway grooves 47 on the track rail 41. Made open on an upper surface 55 of the carriage 44 are holes 56 having female threads that fit on male threads of associated bolts or screws to fasten the carriage 44 to other component such as a work table and the like. Rolling elements such as balls 58 are arranged in load-bearing raceways 57, which are defined between the raceway grooves 47 on the track rail 41 and the raceway grooves 53 in the carriage 44, so as to be allowed to run through the load-bearing raceways 57, thereby moving the slider 42 in a sliding way along the track rail 41. Retainer bands 59 serve continuing to keep the rolling elements 58 against escape out of the carriage 44 even after the slider 42 has been detached from the track rail 41. The rolling elements 58 are charged in the linear motion guide unit in a way allowed to run through a ball-recirculating circuits, each of which includes the load-bearing raceway 58 and a non-loaded raceway that is made up of a return passage 60 bored in the carriage 44 and turnarounds, not shown, formed in the end caps 48, one to each end cap, to connect at opposite ends thereof with the associated load-bearing raceway 57 and return passage 60, thereby completing the ball-recirculating circuit. A grease nipple 61 to apply lubricant into the ball-recirculating circuits is attached to the associated end cap 48 in a way extending outside from the end face of the associated end seal 49.
Nevertheless, the current linear motion guide units, as coming used in the machines that are getting faster in operating speed and cycle, must be further refined on wear proof and quietness in operation. With the prior linear motion guide unit having any separator interposed between two adjoining rolling elements, moreover, any construction that the separator travels with keeping to fit snugly over the associated rolling elements is critical for making sure of steady movement of the rolling elements throughout the ball-recirculating circuit even under modern high-speed operation. For allowing the separator to move with fitting over the associated rolling element, it will be sufficient only to make the separator large in outside diameter, but in this instance it remains a major challenge to make the separators recirculate smoothly together with the associated rolling elements.
Another example of the prior linear motion guide units is disclosed in Japanese Patent Laid-Open No. 281154/1998, in which a separator is arranged between any two adjoining rolling elements to lessen the vibration and noise that might be caused by any regular run of the rolling elements, thus keeping the rolling elements against premature wear. The separator interposed between the two adjoining rolling elements in the linear motion guide unit recited just above, when made large in the outside diameter thereof, is made up of a flat core area and a funnel-shaped peripheral area diverging radially outwardly around the core area. The separator constructed as stated earlier, even though made in the diameter coming into sliding contact with the radially inside curved surface of the associated turnaround, will change place radially outwardly in a direction normal to the running direction of the separator owing to the centrifugal force caused when the separator travels through the turnaround. This behavior will keep the separator from any interference with the radially inside curved surface of the associated turnaround. With the linear motion guide unit stated earlier, however, the separator is apt to experience any wandering in directions normal to the traveling direction of the rolling elements even during the linear travel in any of the load-bearing raceway and return passage because the separator has the flat core area to provide a clearance for allowing the associated rolling element to change place relatively to the concave surface of the separator confronting the rolling element when the separator moves through the turnaround. Thus, the prior linear motion guide unit constructed as stated earlier will get unsteady in the travel of the separator.
Disclosed in Japanese Patent Laid-Open No. 304046/2000 is another example of the prior linear guide bearing arrangement with a separator interposed between any two adjacent rolling elements. With the linear guide bearing arrangement cited above, a curved raceway where the rolling elements are allowed to turn round in sequence is designed to have a radially inside surface of composite curve having more than one curvature different in radius of curvature, rather than an unitary simple semicircular curve. According to the curved raceway constructed as stated earlier, the separator, even if made large in outside diameter, may be kept from any contact at the outside periphery thereof with the radially inside surface of the curved raceway. Nevertheless, the radially inside surface of the curved raceway, because made in the complex shape, introduces expensive machining and forming operations.
Japanese Patent Laid-Open No. 193739/2001 discloses a further another example of the prior linear guide bearing arrangement with a separator interposed between any two adjacent rolling elements, in which balls are accommodated in concaves formed on forward and aft end faces of the associated separator and are allowed to roll with keeping concurrent rolling-contact with both of radially opposing guide surfaces: radially inside and outside curved surfaces of a turnaround. Moreover, the separator is made to have an outer diameter more than the maximum outer diameter allowed when the balls travel through the turnaround with keeping concurrent rolling-contact with both the radially inside and outside curved surfaces of the turnaround, while the radius of curvature defining the curved surfaces in the turnaround is made reduced to keep the separator from any interference with the curved surfaces. With the linear guide bearing arrangement recited just above, even the separator large in outer diameter may travel with no obstacle through the turnaround that has the radially inside curved surface of unitary simple semicircular shape. Besides, the radius of curvature defining the radially inside curved surface in the turnaround is made reduced to the extent where the separator is allowed to roll with no interference with the curved surface.
The prior linear guide bearing arrangement discussed earlier, whether former or latter, has the turnaround where the radially inside curved surface thereof is reduced in radius of curvature so that the curved raceway itself increases somewhat in transverse cross-section. This turnaround construction will allow the rolling elements to roll through there in the absence of rattling sound because the separator large in outer diameter embraces steady the associated rolling elements, whenever the linear guide bearing arrangement is used in horizontality. However, most linear motion guide units are commonly used in every posture: verticality, upside down posture, and so on rather than horizontality. In these instances, both the rolling elements and separators will cause the rattling noise when they run through the widthwise enlarged area of the curved raceway in the turnaround and also the recirculating travel of the rolling elements together with the separators will be liable to unsteady condition.
German Patent DT 2627025 A1 discloses a recirculating-ball steering gear having a separator interposed between any two adjoining rolling elements. The separator is made bulged radially outwardly around the outside periphery thereof to experience a propulsive force that is in a direction at any angle more than 200 even when the separator comes into sliding contact with a radially inside surface of the curved passage. With the recirculating-ball steering gear recited earlier, the separator made large in outer diameter thereof comes into sliding engagement with the radially inside curved surface of the turnaround, encountering much frictional resistance to be much subjected to wear. Thus, it is very tough to expect the smooth recirculation of the rolling elements in the prior recirculating-ball steering gear recited here.
The present invention, therefore, has as its primary object to overcome the major problem discussed earlier and in particular to provide a linear motion guide unit in which a separator is interposed between any two adjoining rolling elements to fit over or embrace the associated rolling elements so as to allow the rolling elements together with the separators to run smoothly, steady through a ball-recirculating circuit without causing rattling sound, thereby making sure of realizing the reduction of noise and wear. Especially, it is often tough for the separators large in outer diameter to travel through the turnaround without seeing any interference with the curved guide surfaces. To cope with this, according to the present invention, a linear motion guide unit is provided in which a radially inside curved surface of the turnaround is made a gutter for relief, which extends in the direction along which the rolling elements run through the turnaround. This construction helps making sure of smooth travel of the separator throughout the ball-recirculating circuit.
The present invention is concerned with a linear motion guide unit comprising; a track rail having a first raceway groove extending lengthwise thereof and a slider arranged for movement relatively to the track rail by virtue of more than one rolling element, the slider being comprised of a carriage made thereon with a second raceway groove confronting the first raceway groove on the track rail to define a raceway between them, where the rolling elements are allowed to run through there, and also made therein with a return passage allowing the rolling elements to run through there, end caps fastened on forward and aft ends of the carriage, one to each end, and each made therein a turnaround that connects the raceway with the return passage to allow the rolling elements to turn round there, and more than one separator interposed between any two adjoining rolling elements to travel together with the rolling elements, wherein the separator has a round outside peripheral surface, and forward and aft end faces that are made concave to fit over the associated rolling elements, and wherein the turnaround formed in the end cap has a radially inside curved surface where a gutter for relief is cut in a way extending circumferentially of the turnaround, thereby allowing the separator to travel through the turnaround without any interference with the radially inside curved surface of the turnaround.
In one aspect of the present invention, a linear motion guide unit is disclosed in which the end cap is comprised of a spacer part having a lug to provide the radially inside curved surface of the turnaround when the spacer part is fastened on the associated end of the carriage, and a major part to provide a radially outside curved surface of the turnaround when mounted on the carriage through the spacer part.
In another aspect of the present invention a linear motion guide unit is disclosed in which the spacer part integral with the lug is joined firmly to the major part with only fitting in a recess formed in the major part, whereby the turnaround is completed.
In another aspect of the present invention, a linear motion guide unit is disclosed in which the gutter for relief is cut in the lug in a way extending circumferentially along a center of the radially inside curved surface of the turnaround.
In another aspect of the present invention, a linear motion guide unit is disclosed in which the spacer part has positioning pins that protrude from the rears of the lugs, which confront the carriage, while the carriage is made on the end face thereof with positioning holes that are bored in opposition to the positioning pins, whereby only fitting the positioning pins into the positioning holes on the end face of the carriage is sufficient to make sure of connection of the spacer part to the carriage.
In another aspect of the present invention a linear motion guide unit is disclosed in which the major part of the end cap has outside joint tongues each of which is adapted to fit into any associated open end of the return passage in the carriage, while the spacer part has inside joint tongues each of which is also allowed to fit into any associated open end of the return passage in the carriage, and wherein the outside and inside joint tongues are mated together in alignment with each other to be connected to the associated return passage.
In a further another aspect of the present invention, a linear motion guide unit is disclosed in which a tubular member of sintered resinous material having cellular texture is nested inside the return passage in the carriage to extend between the lengthwise opposing joint tongues and the tubular member can contain therein lubricant.
In another aspect of the present invention a linear motion guide unit is disclosed in which the concaved surface is made to have a radius of curvature, which is just a little larger than that of the rolling element.
In another aspect of the present invention a linear motion guide unit is disclosed in which the separator is made as thin as possible in thickness left between the concaved surfaces arranged back to back with one another, so that the adjoining rolling elements are separated a little bit away from each other.
In another aspect of the present invention a linear motion guide unit is disclosed in which the separator is made rounded at forward and aft circumferential edges where the outside periphery merges with the concaved surfaces, so that the rounded edges would help make sure of smooth travel of the separator throughout the ball-recirculating circuit even if there were any discrepancy in position between the carriage and the end cap to cause some misalignment between either the load-bearing raceway or the return passage and the associated turnaround for the ball-circulating circuit.
In a further another aspect of the present invention a linear motion guide unit is disclosed in which the track rail has first raceway grooves on the lengthwise sides thereof, one to each side, while the slider fits over and conforms to the track rail for sliding movement relatively to the track rail by virtue of the rolling elements and the separators.
In another aspect of the present invention a linear motion guide unit is disclosed in which the track rail has a pair of lengthwise side walls spaced sidewise apart from and connected with each other, and also made on their sidewise opposing sides with the first raceway grooves, while the slider is accommodated in a guide channel between the side walls of the track rail for sliding movement lengthwise the track rail.
The linear motion guide unit constructed as stated earlier may be adapted well to the track rail of any traverse cross-section, whether I-shape or U-shape. As the separators are allowed to run through the ball-recirculating circuit with keeping fitting over or embracing the associated rolling elements, the linear motion guide unit, even though used at any posture: verticality, upside down posture, and so on rather than horizontality, will cause no distortion owing to the centrifugal force exerted by the running separator, thus raising no rattling sound that might otherwise occur between the rolling elements and the separators. The gutter for relief formed circumferentially on the radially inside curved surface of the turnaround, especially, makes sure of keeping the separator from any interference with the radially inside curved surface of the turnaround, thereby realizing quiet operation and wear-resistance, with even under high-speed, high-cycle sliding motion.
With the linear motion guide unit of the present invention constructed as stated earlier, the separators are each interposed between any two adjoining rolling elements in a way fitting over the associated rolling elements and further the gutter for relief is cut circumferentially in the center of the radially inside curved surface of the turnaround to avoid any interference of the separators with the radially inside curved surface of the turnaround. As a result, the linear motion guide of the present invention, whether used in horizontality or in every posture: verticality, upside down posture, and so on rather than horizontality, makes sure of smooth, steady travel of the rolling elements together with the separators through the ball-recirculating circuit without causing any rattling, thereby realizing quiet operation, wear-resistance and long-lasting service life, with even under high-speed, high-cycle sliding motion.